Upper panel: synthetic profiles of the Mg i b₂ line obtained with the ALC model of the solar atmosphere with (dashed line) and without (dotted line) line blanketing. The solid line is the observed profile. Lower panel: contribution function to line-depression (erg cm³ s^-1 Å^-1) for the 4571 Å line versus height, for the same atmospheric model as in the upper panel, with (dashed line) and without (dotted line) line blanketing.